Why3 vs Z3
Why3
why3.orgZ3
github.comSide by side
| Figure | Why3 | Z3 |
|---|---|---|
| Price from | Free | Free |
| Free plan | Yes | Yes |
| Free trial | — | — |
| Open source | — | — |
| Web | Yes | Yes |
| Windows | Yes | Yes |
| macOS | — | Yes |
| Linux | Yes | Yes |
| Android | — | Yes |
| API | Yes | Yes |
| Self-hosted | Yes | Yes |
| Plans published | 1 | 1 |
| Spec score · Formal Verification Tools | 8.0 (#12) | 7.4 (#26) |
| Downloads | The site lists Debian, Fedora, and Ubuntu packages and links to source release 1.8.2. | The repository links to pre-built binaries for stable and nightly releases. |
| License | TryWhy3 is distributed under the GNU Lesser General Public License version 2.1 with a special linking exception. | The repository states that Z3 is licensed under the MIT license. |
| Purpose | Why3 is a platform for deductive program verification that uses WhyML and external theorem provers to discharge verification conditions. | Z3 is a theorem prover and satisfiability modulo theories (SMT) solver. |
| Support | The project provides a user mailing list, a Zulip chat, and a bug tracking system. | The project wiki says to contact the creator of an external binding package for support issues. |
Plans
In their own words
Why3
Why3 is a platform for deductive program verification. It uses WhyML to express programs and specifications, then works with external automated or interactive theorem provers to discharge verification conditions. WhyML supports preconditions, postconditions, assertions, and loop invariants, alongside logical theories and data structures such as arrays, queues, and hash tables. External provers need to be installed and configured separately. Why3 can be extended with support for new provers and used as a software library through its OCaml API. WhyML programs can be extracted automatically into correct-by-construction OCaml programs, and WhyML is also used as an intermediate language for verification of C, Java, Rust, and Ada. TryWhy3 provides a JavaScript version that runs in a browser. Installation options include Opam, Docker, source compilation, and listed Debian, Fedora, and Ubuntu packages. Its graphical interface saves proof attempts and transformations in an XML file and can replay obsolete attempts. Why3 is free and open source under GNU LGPL 2.1 with a special linking exception. Loop invariant inference is a work in progress, and many features remain very limited.
Z3
Z3 is a theorem prover and satisfiability modulo theories (SMT) solver used in software verification and analysis. SMT-LIB2 is its default input format, and it supports the SMT-LIB format. The project documents bindings or APIs for C, C++, .NET, Java, Go, OCaml, Python, Julia, and JavaScript/TypeScript. Z3 can be built with CMake, vcpkg, or Bazel, and the repository links to pre-built binaries for stable and nightly releases. A project wiki also links to a page for trying Z3 in a browser. It supports proof artifacts and counterexamples, and listed input languages include SMT-LIB2, Rust, Smalltalk, and several of the languages with documented APIs. Z3 is MIT licensed, with downloads and source code available at no charge. Python is required to build it; additional toolchains are needed for Java, .NET, OCaml, and Julia APIs. The README says MSVC builds enable Control Flow Guard and Address Space Layout Randomization by default.